There are a number of known molten bath-based smelting processes.
One molten bath-based smelting process that is generally referred to as the “HIsmelt” process is described in a considerable number of patents and patent applications in the name of the applicant. Another molten bath-based smelting process is referred to hereinafter as the “HIsarna” process. The HIsarna process and apparatus are described in International application PCT/AU99/00884 (WO 00/022176) in the name of the applicant. Other known molten bath-based smelting processes include by way of example only, processes for smelting titania slag and for smelting copper-containing material.
The following description of the invention focuses on the HIsmelt and the HIsarna processes.
The HIsmelt and the HIsarna processes are associated particularly with producing molten iron from iron ore or another iron-containing material.
In the context of producing molten iron, the HIsmelt process includes the steps of:
(a) forming a bath of molten iron and molten slag in a smelting chamber of a smelting vessel;
(b) injecting into the bath; (i) iron ore, typically in the form of fines; and (ii) a solid carbonaceous Material, typically coal, which acts as a reductant of the iron ore feed material and a source of energy; and
(c) smelting iron ore to iron in the bath.
The term “smelting” is herein understood to mean thermal processing wherein chemical reactions that reduce metal oxides take place to produce molten metal.
In the HIsmelt process solid feed materials in the form of metalliferous material and solid carbonaceous material care injected with a carrier gas into the molten bath through a number of lances which are whited to the vertical so as to extend downwardly and inwardly through the side wall of the smelting, vessel and into a lower region of the vessel so as to deliver at least part of the solid feed materials into the metal layer in the bottom of the smelting chamber. The solid feed materials and the carrier gas penetrate the molten bath and cause molten metal and/or slag to be projected into a space above the surface of the bath and brat a transition zone. A blast of oxygen-containing gas, typically oxygen-enriched air or pure oxygen, is injected into an upper region of the smelting chamber of the vessel through a downwardly extending lance to cause post-combustion of reaction gases released from the molten bath in the upper region of the vessel. In the transition zone there is a favourable mass of ascending and thereafter descending droplets or splashes or streams of molten metal and/or slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
Typically, in the case of producing molten iron, when oxygen-enriched air is used, it is fed at a temperature of the order of 1200° C. and is generated in hot blast stoves. If technically pure cold oxygen is used, it is typically fed at or close to ambient temperature.
Off-gases resulting from the post combustion of reaction gases in the smelting vessel are taken away from the upper region of the smelting vessel through an off-gas duct.
The smelting vessel includes refractory-lined sections in the lower hearth and water cooled panels in the side wall and the roof of the vessel, and water is circulated continuously through the panels in a continuous circuit.
The HIsmelt process enables large quantities of molten iron, typically at least 0.5 Mt/a, to be produced by smelting in a single compact vessel.
The HIsarna process is carried out in a smelting apparatus that includes (a) a smelting vessel that includes a smelting chamber and lances for injecting solid feed materials and oxygen-containing gas into the smelting chamber and is adapted to contain a bath of molten metal and slag and (b) a smelt cyclone for pre-treating a metalliferous feed material that is positioned above and communicates directly with the smelting vessel.
The term “smelt cyclone” is understood herein to mean a vessel that typically defines a vertical cylindrical chamber and is constructed so that teed materials supplied to the chamber move in a path around a vertical central axis of the chamber and can withstand high operating temperatures sufficient to at least partially melt metalliferous feed materials.
In one form of the HIsarna process, carbonaceous feed material (typically coal) and optionally flux (typically calcined limestone) are injected into a molten bath in the smelting chamber of the smelting vessel. The carbonaceous material is provided as a source of a reductant and a source of energy. Metalliferous feed material, such as iron ore, optionally blended with flux, is injected into and heated and partially melted and partially reduced in the smelt cyclone. This molten, partly reduced metalliferous material flows downwardly from the smelt cyclone into the molten bath in the smelting vessel and is smelted to molten metal in the bath. Hot reaction gases (typically CO, CO2, H2, and H2O) produced in the molten bath are partially combusted by oxygen-containing gas (typically technical-grade oxygen) in an upper part of the smelting chamber. Heat generated by the post-combustion is transferred to molten droplets in the upper section that back into the molten bath to maintain the temperature of the bath. The hot, partially-combusted reaction gases flow upwardly from the smelting chamber and enter the bottom of the smelt cyclone. Oxygen-containing gas (typically technical-grade oxygen) is injected into the smelt cyclone via tuyeres that are arranged in such a way as to generate a cyclonic swirl pattern in a horizontal plane, i e. about a vertical central axis of the chamber of the smelt cyclone. This injection of oxygen-containing gas leads to further combustion of smelting vessel as resulting M very hot (cyclonic) flames. Incoming metalliferous feed material, typically in the form of fines, is injected pneumatically into these flames via tuyeres in the smelt cyclone, resulting in rapid heating and partial melting accompanied by partial reduction (roughly 10-20% reduction). The reduction is due to both thermal decomposition of hematite and the reducing action of CO/H2 in the reaction gases from the smelting chamber. The hot, partially melted metalliferous feed material is thrown outwards onto the walls of the smelt cyclone by cyclonic swirl action and, as described above, flows downwardly into the smelting vessel below for smelting in the smelting chamber of that vessel.
The net effect of the above-described form of the HIsarna process is a two-step countercurrent process. Metalliferous feed material is heated and partially reduced by outgoing reaction gases from the smelting vessel (with oxygen-containing gas addition) and flows downwardly into the smelting vessel and is smelted to molten iron in smelting chamber of the smelting vessel. In a general sense, this countercurrent arrangement increases productivity and energy efficiency.
The HIsmelt and the HIsarna processes include solids injection into molten baths in smelting vessels via water-cooled solids injection lances.
A key feature of both processes is that the processes operate in a smelting vessel that includes a smelting chamber for smelting metalliferous material and a forehearth connected to the smelting chamber via a forehearth connection that allows continuous metal product outflow from the vessels. A forehearth operates as a molten metal-filled siphon seal, naturally “spilling” excess molten metal from the smelting vessel as it is produced. This allows the molten metal level in the smelting chamber of the smelting vessel to be known and controlled to within a small tolerance—this is essential for plant safety. The molten metal level must (at all times) be kept at a safe distance below water-cooled elements such as solids injection lances extending into the smelting chamber, otherwise steam explosions become possible. It is fir this reason that the forehearth is considered to be an inherent part of a smelting vessel for the HIsmelt and the HIsarna processes.
The term “forehearth” is understood herein to mean a chamber of a smelting vessel that is open to the atmosphere and is connected to a smelting chamber of the smelting vessel via a passageway (referred to herein as a “forehearth connections”) and, under standard operating conditions, contains molten metal in the chamber, with the forehearth connection being completely filled with molten metal.
International publication WO 00/01854 in the name of the applicant describes that a direct smelting vessel that is an example of a vessel that can be used in the HIsmelt and the HIsarna processes and comprises a hearth formed of refractory material and side walls extending upwardly from the sides of the hearth, with the side wall including water cooled panels. The HIsmelt and the HIsarna processes are highly agitated and this results in refractory wear of the upper part of the hearth due to chemical attack and physical wear by molten slag and molten metal washing and splashing against the refractory material in the upper part of the hearth. This wear is greater than is typically experienced in the hearths of blast furnaces in which the hot metal and slag is relatively quiescent.
The present invention enables a significant reduction of such refractory wear of the hearth.
The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere.